Featured Story – The whys and wherefores of on-site machining

Ask any engineer and he or she will probably confirm that the easiest place to conduct valve repairs has to be inside a well-appointed machine shop. After all, this is where staff will have ready access to the tools, machinery and spare parts they are likely to need. However, from time to time it may be necessary to carry out repairs on-site, explains Velan’s Mr. Jérôme Niogret. “Take welded valves for example. Removing them from the installation, transporting them back to our premises for repairs and reinstalling afterwards would be a time-consuming undertaking.

In the oil and gas business sector repair in the field is pretty much mandatory to save time and costs and avoid having to send valves back to our factory.

Obviously if the repair cannot be done by portable machining devices then a transport to our factory or replacement is necessary. Regulations can also be another reason to work on valves in-situ. Valves can for example be installed inside nuclear power plants and therefore be considered as nuclear equipment which should not be removed.”

Asked what kinds of repair work might be required, Mr. Niogret replies: “During regular operations or maintenance issues and defects may be identified relating to specific parts of the valve such as, for example, the sealing surfaces, the body/bonnet junction, the gasket housing, etc. Such defects can cause the valve to lose its own tightness. Machining is then often requested to repair the defect and to restore an appropriate surface finish.”

A decision then has to be taken as to the optimum solution. Mr. Niogret: “the first point to address is to analyse if the necessary repairs can indeed be done on-site with a portable machining device. The repair has to be technically feasible in terms of accuracy

Then of course it is necessary to take time and costs management into account as well as the customer’s schedule. For example, cutting out a valve that is welded to a pipe and sending it back to our factory has a huge impact for customers.”

If the decision is taken that an on-site repair is the most logical option, there can still be plenty of challenges to consider, notes Mr. Niogret. “The first issue is to review the surrounding area to ensure that a portable machining device can actually be installed. Then it is important to protect the surrounding area to prevent any foreign material such as metal chips from being introduced into the pipe. Another point for attention comes when setting up the equipment to ensure all machining will be performed with the required degree of accuracy and thus to protect the valve’s function. And a final issue can be the need to select the right machining device, for example in the case of areas that fall under the ATEX guidelines.”

The actual machining work must definitely be performed by properly-qualified technicians, concludes Mr. Niogret. “At Velan we have a number of staff who are fully trained to repair and machine our valves located in the field. However, as our business scope is worldwide and this type of skillset is rare we sometimes call on sub-suppliers to do the job under our own quality process. As a matter of interest we are also involved in helping to create solutions for additional sectors, such as the LNG industry. We have for example develop a specific portable milling bench in cooperation with SERCO that is geared to repairing LNG valves located on LNG carriers.”